EFFECT OF N2 FLOW-RATE ON TIN FILMS FORMED BY DC PLASMA CVD

Titanium nitride films were deposited on tool steel substrates (JIS SKH51) by DC plasma-assisted chemical vapor deposition. TiCl4, N2, and H2 were used as the reactant gases at a total pressure of 133 Pa. The deposited films were widely investigated for the relationship between N2 flow rate at constant TiCl4 and H2 flow rates and properties of the films; namely, optical, mechanical, structural and compositional properties. Plasma diagnostics was also performed by using a quadrupole mass spectrometer and an optical emission spectrometer in order to investigate the mechanism of titanium nitride formation. It was found that the properties of the deposited films changed systematically with N2 flow rate, and there was an optimum value for desirable properties. The values ranged from 1.67 × 10-6m3·S-1 to 3.33 × 10-6m3·S-1 in N2 flow rate and from 2 to 4 in N2/TiCl4 flow rate ratio. The results indicate that in the range of N2 flow rates below the optimum value, the film properties are affected by the change of the N/Ti ratio, and above the optimum value, by the change of the film structure. Plasma diagnostics suggested that the main species concerned with titanium nitride formation might be Ti and /or Ti+ and NHx(x=1-3). Based on these results, the following model has been proposed. The reactant gases are partially decomposed and activated in a DC positive column to some extent, and the mainly activated in a cathode sheath resulting in the formation of Ti and/or Ti+ and NHx, which may be precursors for the formation of titanium nitride.